Malignant melanoma of the choroid associated with misdiagnosed ocular melanocytosis

Abstract

A 73-year-old white female complained of a darker left eye since childhood, which was interpreted at ophthalmic review some 40 years ago as ‘benign conjunctival melanosis’. Since then, the subject had not consulted an ophthalmologist until this occasion, when she presented with blurry vision OS. On slit-lamp examination, the whole left episclera was seen to show pronounced perivascular melanocytic pigmentation (1, 2). The left iris and choroid also appeared more darkly pigmented. In the periphery, a melanocytic tumour was detected with penetration of the retina and collateral retinal detachment (Fig. 3). The left eye was enucleated. Histological examination revealed an epitheloid cell type melanoma (3, 4) with vitreous invasion and widespread tumour cell seeding 3-5). A dense accumulation of melanocytes as a typical feature of ocular melanocytosis (OM) was found in the uvea, trabecular meshwork, sclera and episclera, especially perivascularly (2, 6). Left eye with brownish subconjunctival pigmentation. Perivascular distribution of episcleral melanocytes. Inset: Masson-trichrome staining: superficial episcleral melanocytes adjacent to blood vessels. The superiorly located choroidal melanoma has penetrated through the retina with strands of malignant cells in the vitreous (arrow). (A) Ultrasonography shows posterior vitreous detachment (arrow). (B) Periodic acid-Shiff staining: epitheloid cell choroidal melanoma penetrates the Bruch's membrane (arrowhead). (C) Masson-trichrome staining: scleral infiltration (arrowheads). Deposits of melanoma cell cover the inferior retina (arrows). Inset: Masson-trichrome staining: melanophages and melanoma cells overlie the retina (arrowhead). Masson-trichrome staining: a typical accumulation of melanocytes in the iris stroma, ciliary body and trabecular meshwork. As a relatively rare condition (with a prevalence of approximately 0.04% among white populations and 0.014% among black populations), congenital OM is often associated with uveal melanomas (Gonder et al. 1982). The lifetime risk of developing uveal melanoma in white OM populations has been estimated to be about 1 : 400, as opposed to 1 : 13 000 for the general white population (Singh et al. 1998). To avoid misdiagnosis as conjunctival melanocytosis (CM), as described in the present report, OM can easily be differentiated from CM. In contrast to OM, CM can be moved over the sclera with a glass rod or cotton tip applicator after topical anaesthesia. Conjunctival melanocytosis is not associated with iris, scleral or choroidal hyperpigmentation. The CM is brownish, whereas episcleral pigment usually has a greyish to bluish tint in OM (Yanoff & Zimmerman 1967; Rummelt & Naumann 1997). Because of an approximately 32-times increased lifetime risk of developing uveal melanomas, patients with OM need to be educated regarding this risk and should be followed with annual lifelong ophthalmoscopic review. This study was supported in part by the Alexander von Humboldt Foundation, Bonn, Germany and the Royal Australian and New Zealand College of Ophthalmologists (RMC).